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Dimerization of aldehydes to carboxylic esters catalyzed by K2[Fe(CO)4]Цcrown ether system.

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APPLIED ORGANOMETALLIC CHEMISTRY, VOL. 7,357-361 (1993)
SHORT PAPER
Dimerization of aldehydes to carboxylic esters
catalyzed by Kz[Fe(CO)&crown ether
system*
Masakazu Yamashitat and Takahiro Ohishi
Department of Applied Chemistry, Faculty of Engineering, Doshisha University, Kamikyo-ku,
Kyoto, 602 Japan
KJFe(C0)J (1) with a crown ether was found to
be an efficient catalyst for the dimerization of
aldehydes to carboxylic esters. Several aromatic
aldehydes including furfural gave the corresponding esters in good yields. This reaction also proceeded intramolecularly to give phthalide from
phthalaldehyde. However, aliphatic aldehydes
gave aldol-condensation products instead of the
corresponding esters. In the reactions of p
substituted benzaldehydes with 1, the reactivity
decreased with increase of the electron-releasing
ability of the substituents. On the basis of these
results, the reaction mechanism including the nucleophilic attack of tetracarbonylferrate dianion to
the carbonyl carbon is discussed.
Keywords: Dimerization, aldehyde, carboxylic
ester, tetracarbonylferrate, synthesis
sis of aldehydes, carboxylic acid derivatives,
ketones and the reduction of a, /3-unsaturated
carbonyl compounds."'
On the other hand, benzyl benzoate 2 is used as
a solvent for artificial musk, as a perfume fixative,
in confectionery, and in chewing-gum flavors. For
these uses, it is necessary to prepare the benzoate
without any contamination by irritants and or
odoriferous materials such as benzyl chlorides
and/or acids.
In the course of our studies on the preparation
of carboxylic esters from aldehydes, we found
that reaction of 1 with 18-crown-6 catalyzes the
dimerization of aromatic aldehydes. In this paper,
we report the details of these ester preparations
using 1 and we also discussion the reaction
mechanism.
RESULTS AND DISCUSSION
INTRODUCTION
Recently, various organic reactions using organometallic compounds as a catalyst or quantitative
reagent have been investigated. Metal carbonyl
complexes are also utilized for this purpose in a
wide variety of synthetic reactions.'-' In particular, iron carbonyl complexes are very useful
because of their low cost and comparative lack of
toxicity compared with other metal carbonyl complexes. Among them, several authors have
demonstrated that alkali-metal tetracarbonylferrates
(M,[Fe(CO),],
MH[Fe(CO),];
M = Na, K) are valuable reagents for the synthe* Synthesis of carboxylic esters from aldehydes using metal
carbonyl anions, Part 1. This work was presented at the 62nd
Annual Meeting of the Chemical Society of Japan, Sapporo,
October 1991.
t Author to whom correspondence should be addressed.
0268-2605/93/050357-05 $07.50
0 1993 by John Wiley & Sons, Ltd.
By way of example, 3 mmol of 1 prepared easily
by reduction of 3 mmol of Fe(CO)s by 2.1-2.5
equivalents of KB(s-C.+H9),H,'2 reacted with
3 mmol of benzaldehyde in tetrahydrofuran
(THF) under an argon atmosphere to give a trace
amount of 2. Two aldehyde groups are transformed into the corresponding alkoxyl and carboxyl functions, existing in combination as an
ester.
In order to raise the yield of this reaction,
several reaction conditions such as temperature
and solvent were examined, but no remarkable
increase of yield was observed. Then, 2 equivalents of 18-crown-6 were added to the reaction
mixture in order to remove the potassium cation
from the tetracarbonylferrate anion. Stirring the
mixture at 60 "C for 6-7 h gave the ester in good
yield (Scheme 1). This reaction proceeded by
means of a catalytic amount of 1 and the crown
Received 25 January I993
Accepted 20 April I993
M YAMASHITA AND T OHISHI
358
Table 1 Reaction of benzaldehyde with K2Fe(CO)4
Reaction conditions
Run
1
2
3
4
5
Aldehyde/K2Fe(CO),
ratio
1
5
10
15
50
Temp. ("C)
Time (h)
Yield (%.)'
60
60
60
60
60
4
7
24
6
40
70Sb
62.9b
71.9b
45.T
8O.Ob
'Based on the amount of aldehydes. bYields were determined by GC.
Isolated yield.
1
scheme 1
ether. This effect is considered to be due to the
generation of naked [Fe(CO),]'- by removal of
K+ from the tight ion-pair 1. The results are
shown in Table 1.
Under similar conditions, several aromatic
aldehydes gave the corresponding esters. The
results of these reactions are listed in Table 2.
Benzaldehyde and p-chlorobenzaldehyde gave
the corresponding ester 2 and 6 in 170-177%
yield. In contrast, p-tolualdehyde and p anisaldehyde, having electron-releasing substituents, produced esters 11 and 5 in lower yield,
and the substantial amounts of starting materials
were recovered. The by-products obtained in
these reactions were small amounts of alcohols
such as benzyl alcohol. Interestingly, when furfural was used, furfuryl alcohol was the main
product (32.7%), showing the reduction of the
carbonyl group. Moreover, this reaction also proceeded intramolecularly to give phthalide (14)
from phthalaldehyde.
On the other hand, the treatment of aliphatic
aldehydes with 1 gave completely different
results. Hexanal afforded 2-butyl-2-octenal 13
and the corresponding hexyl hexanoate was not
obtained. The apparent disparity is due to the
basicity of [Fe(CO),]*- [the basicity of
Fe(CO),r- is estimated to be about that of the
OH- ion '1. In the case of aliphatic aldehydes 1
works as a base and an aldol-condensation reaction proceeds preferentially.
When terephthalaldehyde is treated with the
catalyst, the corresponding polyester compounds
are expected to be formed. The reaction was
CATALYTIC DIMERIZATION OF ALDEHYDES
2
0
4
Time @)
359
6
.,
F%nre 1 Yields of esters vs time plots for the reaction of 1
with aldehydes in THF, at 60°C under argon: A , p chlorobenzaldehyde; 0,benzaldehyde;
p-tolualdehyde;
A , p-anisaldehyde.
examined under several reaction conditions; it
proceeded smoothly and the starting material disappeared within 6 h. Tarry material was obtained
as a product in each case, although it was not
analyzed.
In the reaction of p-substituted benzaldehydes
using 1, the remarkable influence of the substituents was observed on the reaction rates. The
yields of esters vs time plots for these reactions
are shown in Fig. 1. The order of their reactivities
is as follows: p-ClC6H4CH0> C6H5CH0>
p-CH,C&,CHO >p-CH,OC,H,CHO. The reactivity decreased with increase of the electronreleasing property of the substituents. This suggests that the reaction is attributed to the electron
density on the carbonyl carbon of the aldehydes.
Next, an equimolar mixture of two different
aldehydes which have different electron density
on their carbonyl carbon was treated with 1
(Scheme 2). In each case, the main product was
formed by reaction of the aldehyde pair having
lower electron density on the carbonyl carbon
than the others. An ester derived from the aldehydes which has higher electron density on its
carbonyl carbon than the other was formed in
very low yield, or not formed.
On the basis of these results, the reaction
mechanism is discussed (Scheme 3). First,
[Fe(C0),l2- attacks the carbonyl carbon of the
aldehyde nucleophilically to give an adduct A.
The addition of the second aldeh de to A is
followed by the loss of the [Fe(CO),f to give the
esters. The [Fe(CO)4]2-attacks the carbonyl carbon of the other aldehyde again as a catalyst. This
mechanism is supported by the investigations of
Table 2 Reaction of aldehydes with K,Fe(CO),
Conditions
Aidehyde
Run
(-01)
K,Fe(CO),
(mmol)
Temp.
("C)
Time
(h)
60
60
60
60
6
4
4
45
60
24
Yield
(Yo)"
Products
0
5
Furfural(9)
3
2; R = H
6; R=CI
11: R=Me
70Sb
68.7b
14.1b
8.Ob
3.4c
0
6
n-Hexanal(l5)
3
60
4
13; CHj(CH2)jCCHO
50.7'
II
CH(CH&CHj
7
8
o-Phthalaldehyde(l5)
Terephthalaldehyde(15)
I
1
60
60
22
18
14; Phthalide
-d
17.1b
-
'Based on the amount of aldehydes. Yields were determined by GC. Isolated yields. Tarry materials were obtained.
M YAMASHITA AND T OHISHI
360
the effect of substituents upon the reactivity of psubstituted benzaldehydes. It is roughly similar to
that of the well-known variations of the baseinduced dismutation of aldehydes.l4
EXPERIMENTAL
General
'H NMR spectra were recorded with a Hitachi
R-600 FT-NMR spectrometer operating at
60 MHz. Peak positions are reported in parts per
million relative to tetramethylsilane internal
standard. Spectra which were recorded without
resonance decoupling have peaks reported as
singlet (s), doublet (d), triplet (t), quartet (4) or
multiplet (m). Infrared (IR) spectra were
recorded on a Hitachi 260-10 spectrometer as
KBr pellets, Nujol (for solids) or liquid film (for
liquids). Mass spectra were recorded on a Hitachi
M-80B or Shimazu GCMS-QP2000A instrument.
Gas chromatography was performed on a
Shimazu GC-14A model equipped with a capillary
column
(CBP 1-W12-100,
0.53 mm
i.d. X 12m) using helium as a carrier gas. All
melting points were determined with Yanagimoto
micro-melting-point apparatus and are uncorrected. Column chromatography was done with
E. Merck silica gel 60(230-400-mesh). Analytical
thin-layer chromatography (TLC) was done with
E. Merck reagent silica gel 60 F-254 with a
0.25 mm thickness. Tetrahydrofuran (THF) was
dried and distilled under an argon atmosphere
from potassium-bemophenone just before use.
The aldehydes were all commercial products;
they were dehydrated over calcium sulphate and
distilled before use. Potassium tri-s-butylhydroborate was purchased from Aldrich
Chemical Co. as a 1.0 M THF solution under the
trade name K-selectride. Pentacarbonyliron and
18-crown-6 were commercial products and were
used without further purification.
scheme 3
Preparation of 1
Under an argon atmosphere, Fe(CO), (0.13 ml,
1mmol) was added to the THF solution (2.2 ml)
of 1 . 0 K-selectride
~
in a reactor. The reaction
mixture was refluxed for 4 h. After cooling, the
resultant colorless precipitate was washed with
THF (3 x 10ml) in the reaction flask.
Preparation of carboxylic esters
In a typical procedure, 2 mmol of 18-crown-6and
aldehydes were added to a solution of 1mmol of 1
in 10ml tetrahydrofuran, and the mixture was
stirred at 60°C for a certain reaction time under
an argon atmosphere. Then the mixture was
poured into 30ml of water and extracted with
diethyl ether. After drying over magnesium sulphate, the organic extracts were concentrated.
The residual crude products were purified by
column chromatography. The esters thus
obtained were identified by means of their spectral data (IR, NMR and mass spectra) and by
comparison of the GLC retention time with those
of authentic samples; the yields were determined
using internal standards. All products gave satisfactory analyses.
Benzyl benzoate (2)
IR (liquid film) 3050, 1730, 1460, 1280, 1120,
720cm-'; 'H NMR(CDC1,) 6=5.34 (2H, s,
OCH?), 7.08-8.18 (lOH, m, aromatic H); GC MS
mlz (relative intensity) 212 (M+, 23), 105 (loo),
91 (56), 77 (40),51 (25).
p-Chlorobenzylp-chlorobenzoate (6)
IR (Nujol) 1740, 1610, 1290, 1220, 790cm-'; 'H
NMR (CDClJ 6=5.30 (2H, S, OCHZ), 7.23-8.12
(8H, m, aromatic H); GC MS m / z (relative intensity) 280 (M+,9), 139 (48), 125 (30), 86 (loo), 58
(27). M.P. =63-64 "C.
p-Methylbenzyl p-methylbenzoate (11)
IR (Nujol) 1730, 1620, 1280, 1180, 1100, 820,
760cm-'; 'H NMR (CDC13) 6=2.29 (6H, s,
2 x CH3), 5.20 (2H, s, OCHJ 6.95-8.10 (8H, m,
aromatic H); GC MS m/z(relative intensity) 240
(M', 30), 119 (loo), 105 (48), 91 (27), 65 (14).
M.P. =35-37 "C.
p-Methoxybenzyl p-methoxybenzoate (5)
IR (liquid film) 3000, 2860, 1720, 1620, 1520,
1270, 1180, 1120, 780cm-'; 'H NMR (CDCI,)
6 = 3.80 (3H, s, OCH,), 3.81 (3H, s, OCH,), 5.24
(2H, s, OCH2), 6.74-8.10 (8H, M, aromatic H).
CATALYTIC DIMERIZATION OF ALDEHYDES
GC MS mlz (relative intensity) 272 (M', 15), 135
(43), 121 (loo), 77 (26).
Furfuryl2-furancarboxylate (12)
IR (liquid film) 2940, 1720, 1480, 1300, 1180,
1120,760cm-'; 'H NMR (CDCl,) 6 = 5.12 (2H, s,
OCH2),6.15-7.60 (6H, m, furan H). GC MS mlz
(relative intensity) 192 (M+, 15), 95 (12), 91
(100).
2-Butyl3-octenal (13)
IR (liquid film) 2950,1700, 1480, 1280,800cm-';
'H NMR (CDCl,) 6=0.70-1.10 (6H, m,
2 x CH,), 1.10-2.60 (14H, m, 7 x CH2),6.40 (lH,
t, CH=C), 9.30 (lH, s, CHO). GC MS rnlz
(relative intensity) 182 (M+, 14), 139 (21), 125
(15), 111 (36), 83 (33), 55 (100).
Phthalide (14)
IR (Nujol) 1760, 1300, 1240, 1080, 1020,
760cm-'; 'H NMR (CDC13) 6=5.30 (2H, s,
CH20),7.35-8.10 (4H, m, aromatic H). GC MS
mlz (relative intensity) 134 (M', 29), 118 (20),
105 (loo), 77 (38), M.p.=72-74"C.
Benzyl p-methoxybenzoate (3)
IR (liquid film) 3000, 1740, 1620, 1280, 1180,
1120, 1040, 780cm-'; 'H NMR (CDCl,) 6=3.80
(3H, s, OCH,), 5.30 (2H, s, OCH2), 6.75-8.15
(9H, m, aromatic H). GC MS rnlz (relative intensity) 242 (m+, lo), 197 (2), 135 (loo), 91 (48).
pMethoxybenzy1 benzoate (4)
IR (liquid film) 3000, 1740, 1640, 1300, 1200,
1140,740cm-'; 'H NMR (CDCl,) 6 = 3.80 (3H, s,
OCH,), 5.29 (2H, s, OCH2), 6.75-8.20 (9H, m,
aromatic H). GC MS mlz (relative intensity) 242
(M+, 25), 121 (loo), 105 (46), 77 (52).
p-Chlorobenzyl benzoate (7)
IR (liquid film) 1740, 1520, 1480, 1300, 1120,
730cm-'; 'H NMR (CDC1,) 6=5.28 (2H, s,
OCH2) 7.15-8.18 (9H, m, aromatic H). GC MS
mlt (relative intensity) 246 (M+, 14), 125 (47),
105 (loo), 77 (48).
Benzyl p-chlorobenzoate (8)
IR (liquid film) 1760, 1620, 1430, 1300, 1120,
780cm-'; 'H NMR (CDCI,) 6=5.32 (2H, s,
OCH2), 7.10-8.12 (9H, m, aromatic H). GC MS
rnlz (relative intensity) 246 (M', 20), 139 (88),
111(26), 91 (loo), 75 (30).
p-Methoxybenzyl p-chlorobenzoate (9)
IR (Nujol) 1740, 1620, 1600, 1280, 1100,
760cm-'; 'H NMR (CDCI,) 6=3.77 (3H, s,
361
OCH,), 5.24 (2H, s, OCH,), 6.72-8.10 (8H, m,
aromatic H). GC MS rnlz (relative intensity) 276
(M+, 16), 139 (16), 121 (10). M.p.=34-36"C.
pChlorobenzyl p-Methoxybenzoate (10)
IR (KBr) 170,1600,1500,1260,1180,800cm-';
'H NMR (CDC1,) 6=3.82 (3H, S, OCH,), 5.28
(2H, s, OCH2), 6.70-8.20 (8H, m, aromatic H).
GC MS mlz (relative intensity) 276 (M+, 8), 231
(3), 135 (loo), 125 (39). M.p.=78-8O0C.
CONCLUSIONS
1 and the 18-crown-6 system was found to be an
efficient catalyst for the conversion of aromatic
aldehydes to carboxylic esters. This reaction proceeded not only intermolecularly but also intramolecularly to give the esters and lactones in
good yields and, as 1 was easily prepared from
Fe(CO)5 and K(s-C4H,)$3H, it may become a
good synthetic method for carbooxylic esters
from aldehydes.
REFERENCES
1. McQuillin, F J, Parker, D G and Stephenson, G R
Transition Metal Organometallics for Organic Synthesis,
Cambridge University Press, Cambridge, 1991
2. Hamngton, P J Transition Metals in Total Synthesis, John
Wiley & Sons, New York, 1991
3. Crabtree, R H The Organometallic Chemistry of the
Transition Merals, John Wiley & Sons, New York, 1988
4. Collman, J P Acc. Chem. Res., 1975,342
5. Finke, R G and Sorrel, T N Org. Synth., 1988, Coll. Vol.
VI: 807
6. Yamashita, M, Watanabe, Y, Mitsudo, T and Takegami,
Y Bull. Chem. SOC.Jpn., 1976,49 3597
7. Yamashita, M, Miyoshi, K, Nakazono, Y and Suemitsu,
R Bull. Chem. SOC.Jpn., 1982, 55: 1663
8. McMurry, E and Andrus, A Tetrahedron Len., 1980: 4687
9. Yamashita, M, Yamamura, S, Kurimoto, M and
Suemitsu, R Chem. Len., 1979: 1067
10. Alper, H, Marchand, B and Tanaka, M Can 1. Chem.,
1979, 57: 598
11. Yamashita, M, Tashika, H and Uchidea, M Bull. Chem.
SOC. Jpn., 1992,65:1257 and references cited therein.
12. Gladysz, J A and Tam, W J . Org. Chem., 1978,43: 2279
13. Hieber, Wand Hubel, W Z . Electrochem., 1953,57: 235
14. Geissman, T A Organic Reactions, vol2, Adams, R (ed),
John Wiley & Sons, New York, 1957
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